1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device including a patterned spacer and a method of fabricating the same.
2. Discussion of the Related Art
Recently, LCD devices have been widely utilized because of thin profile, light weight and low power consumption. Among them, an active matrix LCD device, which has thin film transistors and pixel electrodes arranged in a matrix form to provide high resolution and superiority in displaying moving images, is the subject of significant research and development. The LCD device typically includes a first substrate, a second substrate, and a liquid crystal layer that is interposed between the first and second substrates. The first substrate, also referred to as an array substrate, further includes a thin film transistor (TFT) and a pixel electrode. The second substrate, also referred to as a color filter substrate, further includes a color filter and a common electrode.
FIG. 1 is a schematic perspective view of an LCD device according to the related art. As shown in FIG. 1, an LCD device 1 includes a first substrate 10 and a second substrate 20 that face each other, and a liquid crystal layer 30 that is interposed between the first and second substrates 10 and 20. The first substrate 10 further includes a plurality of gate lines 13, a plurality of data lines 15, a TFT Tr and a pixel electrode 17. The plurality of gate and data lines 13 and 15 are arranged crossing each other, thereby defining a pixel region P. The TFT Tr is formed at a crossing portion of the gate and data lines 13 and 15. The pixel electrode 17 is formed on the pixel region P and connected to the TFT Tr. The second substrate 20 further includes a color filter 23, a common electrode 27 and a black matrix (not shown). Moreover, a seal pattern (not shown) is utilized to seal edges of the first and second substrates 10 and 20, and a plurality of ball spacers (not shown) are arranged between the first and second substrates 10 and 20, thereby spacing the first substrate 10 apart from the second substrate 20. In other words, the first and second substrates 10 and 20 are bonded with the seal pattern at the edges and have the ball spacers sandwiched in-between. Then, the liquid crystal layer is thus formed in a space created by the ball spacers. The plurality of ball spacers each have a spherical shape and are dispersed onto either the first substrate 10 or the second substrate 20. However, the plurality of ball spacers are apt to gather close to each other, thereby making it difficult to evenly disperse the plurality of ball spacers. Also, disposing the plurality of ball spacers in the pixel region P may cause a light leakage. To resolve the above-mentioned problems, a patterned spacer is suggested. The patterned spacer may be fixed either to the array substrate 10 or the color substrate 20.
FIG. 2. is a plane view of an LCD device having the patterned spacer according to the related art. As shown in FIG. 2, a gate line 43 and a data line 55 are formed on the first substrate 40 and cross each other to define a pixel region P. In the pixel region P, a TFT Tr and a pixel electrode 67 are formed. The TFT Tr includes a semiconductor layer 50, a gate electrode 45, a source electrode 58 and a drain electrode 60. The gate electrode 45 is connected to the gate line 43, and the source electrode 58 is connected to the data line 55. The drain electrode 60 is spaced apart from the source electrode 58 and is connected to the pixel electrode 67 through a drain contact hole 65. The pixel region P includes three sub-pixel regions, which are corresponding to three sub-color filters (not shown) of the color filter layer (23 of FIG. 1), respectively. The plurality of patterned spacers 83 are arranged on the array substrate 40 such that they are separated from each other. The array substrate 40 and the second substrate (20 of FIG. 1) are attached with a gap created by the plurality of patterned spacers 83. It can be understood that the plurality of patterned spacers 83 are formed on the gate line 43, not in an active region AA consisting of a plurality of pixel regions P, thereby preventing light leakage.
FIG. 3 is a cross-sectional view of the related art LCD device, taken along the line III-III of FIG. 2. As shown in FIG. 3, the gate electrode 45 and the gate line 43 are formed on the first substrate 40, and a gate insulating layer 47 is formed on the gate electrode 45 and the gate line 43. The semiconductor layer 50 consists of an active layer 50a and an ohmic contact layer 50b and is formed corresponding to the gate electrode 45 on the gate insulating layer 47. The source electrode 58 and the drain electrode 60 are formed on the semiconductor layer 50 such that they are spaced apart from each other and respectively connected to the ohmic contact layer 50b. Also, a passivation layer 63 having the drain contact hole 65 is formed on the source and drain electrodes 58 and 60, and the pixel electrode 67 is formed on the passivation layer 63 and connected to the drain electrode 60 through the drain contact hole 65. A black matrix 73, the color filter layer 76 and a common electrode 79 are sequentially formed on a second substrate 70 facing the first substrate 40. Specifically, the black matrix 73 having a plurality of openings is formed on the second substrate 70, and then the color filter layer 76 is formed on the black matrix 73 and covers the plurality openings. As shown in both of FIGS. 2 and 3, the color filter layer 73 includes three sub-color filters 76a, 76b and 76c of red, green and blue colors. The common electrode 79 is formed of a transparent material and covers the color filter layer 73.
A plurality of patterned spacer 83 are arranged apart from each other between the common electrode 79 of the second substrate 70 and the passivation layer 63 of the first substrate 40. In other words, the plurality of patterned spacers 83 are connected to the common electrode 79 and the passivation layer 63. Then, the liquid crystal layer 90 is thus interposed between the first and second substrates 40 and 70. Herein, the plurality of patterned spacer 83 are formed on the second substrate 70 because a process of fabricating the second substrate 70 is less complicated than that of fabricating the first substrate 40. However, when the related art LCD device having the patterned spacer 83 is erect under a high temperature ambience, since an expansion rate of the patterned spacer 83 is less than that of the liquid crystal layer 90 and an expansion rate of the first and second substrates 40 and 70, the liquid crystal layer 90 slips down due to gravity. In other words, when the LCD device is driven under high temperature ambience, the patterned spacer 83 may be separated from the first substrate 40 or/and the second substrate 70, thereby failing to maintain the cell-gap between the first and second substrates 40 and 70. Moreover, since the patterned spacer 83 has lower elasticity than the ball spacer, the patterned spacer 83 can be distorted by even a low impact. Accordingly, when an active region of the LCD device, which is a region displaying images, is touched, flaws such as thickness non-uniformity of the liquid crystal layer occur. To resolve the above-mentioned problems, a double-structure patterned spacer that has two spacers with different heights is suggested.
FIG. 4 is a cross-sectional view showing an LCD device having the double-structure patterned spacer according to the related art. Since the LCD device of FIG. 4 is similar to the LCD device of FIG. 3 except for the double-structure patterned spacer, the description regarding the other parts of the LCD device of FIG. 4 is omitted.
As shown in FIG. 4, the double-structure patterned spacer consists of first and second patterned spacers 183a and 183b that are formed on a common electrode 179 of a second substrate 170. The first patterned spacer 183a has a first height h1 and contacts both a passivation layer 163 of a first substrate 140 and the common electrode 179 of the second substrate 170. The second patterned spacer 183b has a second height h2 shorter than the first height h1, and only contacts the common electrode 179 of the second substrate 170. In other words, the second patterned spacer 183b is separated from the passivation layer 163 of the first substrate 140.
According to the related art, a gap between the passivation layer 163 and the second patterned spacer 183b is more than about 0.4 μm. That is, a height difference between the first and second patterned spacers 183a and 183b is more than about 0.4 μm. Since a distance between the passivation layer 163 and the second patterned spacer 183b is too far, the above-mentioned flaws can not be effectively prevented. It is required that the height difference between the first and second patterned spacers 183a and 183b is less than 0.4 μm. However, since the first and second patterned spacers 183a and 183b are formed of an organic insulating material of several micrometers through at least two mask processes to obtain the height difference, it is practically difficult to shorten the height difference, and also it causes an increase in production costs of the LCD device.